1. Field of the Invention
The present invention relates to a brush encoder that is widely used as a position detector for detecting a relative position between two members, one of which moves relative to the other, and more specifically relates to a fixing structure of a brush of the brush encoder.
2. Description of the Related Art
A photographing lens is often provided therein with a brush encoder to detect a focal length or a photographing distance. For instance, one of two members of the photographing lens (e.g., two rotational barrels), one of which moves relative to the other, serves as a brush support member which supports a brush of the brush encoder while the other member serves as a coding-plate support member which supports a coding plate of the brush encoder so that resilient contact strips of the brush come in sliding contact with the coding plate. The number of the resilient contact strips (i.e., the number of conductive segments of the coding plate) depends on the number of pieces of positional information needed for the two members.
In such a conventional brush encoder, the resilient contact strips are brought into pressing contact with the coding plate by fixing the base portion of the brush to the brush support member with a set screw or an adhesive.
Accordingly, in such a conventional brush encoder, a fixing member and a fixing procedure are required to fix the brush to the brush support member. In addition, if the fixing member comes off, the brush also comes off, which causes a loss of the operation of the brush encoder.
An object of the present invention is to provide a brush encoder in which no fixing member for fixing the brush to the brush support member is necessary. Another object of the present invention is to provide a brush encoder in which there is no possibility of the brush coming off even if the fixing member, via which the brush is fixed to the brush support member, comes off in the case of using a fixing member.
To achieve the object mentioned above, according to an aspect of the present invention, a brush encoder is provided, including a coding-plate support member to which a coding plate is fixed; and a brush support member, movable relative to the coding-plate support member, to which a brush is fixed, the brush having a base portion and resilient contact strips extending from the base portion, the contact strips being in sliding contact with the coding plate. The brush support member includes a support surface to which the base portion of the brush is mounted; at least one through slot through which the resilient contact strips of the brush extend toward the coding-plate support member to come in sliding contact with the coding plate; and a fulcrum portion, which contacts the base portion of the brush in the vicinity of a border between the base portion and the resilient contact strips, so as to serve as a fulcrum about which the brush is biased to rotate in a direction to make the base portion contact the support surface when the resilient contact strips are pressed against the coding plate so as to be elastically deformed thereby.
Preferably, the at least one through slot includes a plurality of through slots through which the resilient contact strips of the brush extend toward the coding-plate support member, respectively. The fulcrum portion includes at least one groove in which an end of the base portion which is adjacent to the resilient contact strips is partly inserted.
Preferably, the at least one groove of the fulcrum portion is formed on the brush support member at a position corresponding to a substantially center of the plurality of through slots in a direction perpendicular to a longitudinal direction of the plurality of through slots.
In an embodiment, the coding-plate support member is formed as a first ring-shaped member, and the brush support member is formed as a second ring-shaped member, wherein the coding plate is fixed to a peripheral surface of the first ring-shaped member.
In an embodiment, the coding-plate support member is formed as a first ring-shaped member, and the brush support member is formed as a second ring-shaped member, wherein the coding plate is fixed to an outer peripheral surface of the first ring-shaped member; and the support surface, to which the base portion of the brush is mounted, is formed on an outer peripheral surface of the second ring-shaped member.
In an embodiment, the coding-plate support member is formed as a first ring-shaped member, and the brush support member is formed as a second ring-shaped member, wherein the coding plate is fixed to an end face of the first ring-shaped member. The support surface, to which the base portion of the brush is mounted, is formed on an end face of the second ring-shaped member, and extends radially inwards.
Preferably, the brush support member further includes at least one protrusion which protrudes from the support surface; the at least one protrusion corresponding with at least one hole, in which the at least one protrusion is fitted, formed on the base portion of the brush.
Preferably, the base portion of the brush includes a bent portion at the end of the base portion.
According to another aspect of the present invention, a brush encoder is provided, including a coding plate having conductive traces formed in a predetermined pattern; a brush having resilient contact strips which come in sliding contact with the conductive traces of the coding plate, respectively; a coding-plate support member and a brush support member which move relative to each other, the coding plate and the brush being fixed to the coding-plate support member and the brush support member, respectively. The brush support member includes a support surface to which a base portion of the brush is mounted; through slots formed adjacent to the support surface to extend parallel to each other in a longitudinal direction of the coding plate, the resilient contact strips of the brush extend toward the coding-plate support member through the through slots to come into sliding contact with the conductive traces, respectively; and at least one insertion slot which is formed between the base portion and the through slots and in which an end of the base portion which is adjacent to the resilient contact strips is partly inserted. The brush is biased to rotate about the at least one insertion slot in a direction to make the base portion contact the support surface when the resilient contact strips are pressed against the coding plate so as to be elastically deformed thereby.
The present disclosure relates to subject matter contained in Japanese Patent Application No.2000-396724 (filed on Dec. 27, 2000) which is expressly incorporated herein by reference in its entirety.